A device for emptying a film tube containing a flowable substance is known from U.S. Pat. No. 5,332,122, wherein the dispensing end of the tube carries a ring having a conical sealing surface, the device including a cylindrical housing for receiving the film tube between a displaceable piston and a cap. A dispensing opening is provided in the cap which has an annular surface for engaging the conical sealing surface of the ring mounted on the tube.
For operating the known device, the film tube is inserted into the cylindrical housing from the front or rear end thereof, whereupon the cap is connected to the front end of the housing and the piston is inserted into the rear end, this time, the conical sealing surface of the ring comes into contact with an engaging portion provided in the cap, which is intended to make sure that the tube, which has been cut open at a position beyond the ring, can be emptied only through the dispensing opening of the cap while preventing any material from reaching the space between the cap, the tube and the container. Since the sealing force is derived from the dispensing pressure produced by advancement of the piston, it is automatically increased whenever dispensing pressure is applied.
Proper operation of the known device requires the ring to be correctly mounted on the film tube in the radial and angular directions. Since the tube is manufactured from a length of tubular sheet material and has its ends simply squeezed and sealed by clips, inaccuracies in mounting the ring on the crimped tube end by means of adhesive cannot be avoided. In practice there will be cases where the ring and thus its conical sealing surface are disposed obliquely or eccentrically with respect to the axis of the sealing counter surface provided in the cap. This may result in incomplete sealing.
If the tube contains a substance of relatively low viscosity, such as a fresh catalyst, there is a chance for the substance to start flowing out even at low pressure exerted on the piston and before a sufficient pressure has been established between the sealing surfaces of the ring and the cap. In this situation, the escaping substance may reach the area of the sealing surfaces and eventually prevent a sufficient seal.
It may further happen in practice that the outer diameter of the film tube is at its upper tolerance limit, or that the outer surface of the tube or the inner surface of the cylindrical housing is polluted. In this case, if the tube is inserted into the housing from the rear, it may become jammed and may not reach its foremost position, so that the sealing surface of the ring does not reach the counter surface of the cap. The same may happen when the tube is inserted from the front and is moved too far into the housing. No proper sealing is ensured in these cases.
The described seal at the front end of the film tube is of particular significance when the tube contains one of two or more components which are simultaneously dispensed to prepare a mixture of substances. In such a case, an exact mixing ratio is essential to achieve a finished material of desired properties; this requires a predetermined quantity of each component to be dispensed completely.
A further reason why the seal is important is the fact that in dispensing devices of the type under consideration, only the tube is designed as a disposable item whereas the housing and the cap should be parts of a re-usable device. Pollution of the interior of the housing and of the rear area of the cap may render these parts of the device useless.